1. Field of the Invention
The present invention relates to an engine control device, and more particularly to an engine control device which can retrieve data in a short amount of time and reduce the time required for execution of various operations.
2. Description of the Background Art
In order to improve the output, fuel economy, exhaust gas purification, etc. of an automotive engine, the proper control of the air-fuel ratio, the ignition timing, the exhaust gas recirculation, etc. which influence the combustion of the engine are required.
In a conventional engine control system, output data from various sensors is input as digital signals to an electronic control device, and preliminary data that has been stored in the device is retrieved as digital signals in response to the introduced digital signals. Then, the preliminary data that corresponds to the detected digital signals is read out, and various actuators are controlled in response to the signal that is read out.
An example of a retrieving method for a conventional engine control system is disclosed in Japanese Pat. Publication No. 63-18017. In this publication, the retrieving time of the data is based on a maximum value of the engine speed or the load. Accordingly, as the engine speed or the load increases, the retrieving time for retrieving data decreases. The retrieval time is thereby reduced for executing of various operations based on the engine speed or the load.
The retrieving method described above has the following problem. When an electronic fuel injection device is controlled which requires a table retrieval at every given crank angle, for example, the retrieving method described above is advantageous at high engine speeds since the retrieving operation is preferentially conducted in response to the high engine speeds, and the retrieving time is reduced. However, when the engine speed is low, the retrieving time is increased. Accordingly, many kinds of arithmetic operations cannot be executed in the same amount of time.
In contrast, if the engine speeds are retrieved from a low value thereof, the retrieving time at high engine speeds cannot be reduced. Because it is normally desirable to reduce the retrieving time at high engine speeds, such a long retrieving time of the low engine speeds is disadvantageous.